Take any standard CRS and change few parameters like Units or name etc to make it non standard
For example;
PROJCS["Wyoming_State_Pl_NAD_1927",GEOGCS["GCS_North_American_Datum_1927_-_NADCON_ConUS",DATUM["D_North_American_Datum_1927",SPHEROID["Clarke_1866",6378206.4,294.9786982]],PRIMEM["Greenwich",0.0],UNIT["Degree",0.01745329251994]],PROJECTION["Transverse_Mercator"],PARAMETER["Scale_Factor",0.9999412],PARAMETER["False_Northing",0.0],PARAMETER["Central_Meridian",-107.3333333],PARAMETER["False_Easting",500000.0],PARAMETER["Latitude_Of_Origin",40.66666667],UNIT["Foot_US",0.30480060960121924]]